This invention relates to an electrostatographic printing machine, and more particularly concerns an apparatus for forming copies of an original document wherein selected portions of the copy are highlighted in a color other than the remainder thereof.
In electrostatographic printing, an electrostatic latent image is created and reproduced in viewable form. The process of electrostatographic printing includes electrophotographic and electrographic printing. Electrophotographic printing employs a photosensitive medium to form, with the aid of electromagnetic radiation, an electrostatic latent image. Contrawise, electrographic printing employs an insulating medium to form, without the aid of electromagnetic radiation, an electrostatic latent image. Hereinafter, an electrophotographic printing machine will be described as an illustrative embodiment of the invention concept described in the present application.
Electrophotographic printing, as disclosed in U.S. Pat. No. 2,297,691 issued to Carlson in 1942, describes exposing a charged photoconductive member to a light image of an original document. The irradiated areas of the photoconductive surface are discharged to record thereon an electrostatic latent image corresponding to the original document. Development of the electrostatic latent lamp is achieved by bringing a developer mix into contact therewith. A typical developer mix employs colored heat settable plastic particles known generally as toner particles, which are mixed with ferromagnetic granules, i.e., carrier granules. The developer mix is selected such that the toner particles acquire the appropriate charge relative to the electrostatic latent image recorded on the photoconductive surface. As the developer mix is moved into contact with the photoconductive surface, the greater attractive force of the electrostatic latent image causes the toner particles to be separated from the carrier granules and to adhere to the electrostatic latent image. The toner powder image adhering to the electrostatic latent image is, then, transferred to the sheet of support material. A suitable sheet of support material is paper, or a thermoplastic sheet, amongst others. Subsequently, the toner powder image is permanently affixed to the sheet of support material or copy sheet.
Essentially, multi-color printing repeats the foregoing process a plurality of cycles. For example, U.S. Pat. No. 3,531,195 issued to Tanaka, et al. in 1970 discloses a multi-color electrophotographic printing machine. As recited therein, the light image is filtered to record an electrostatic latent image on the photoconductive surface corresponding thereto. The electrostatic latent image is then developed with toner particles complimentary in color to the filtered light image. The toner powder image is then transferred to the sheet of support material. The foregoing process is repeated for successively differently colored light images. As described in Tanaka, each toner powder image is fused after being transferred to the sheet of support material. However, one skilled in the art will realize that all of the toner powder images may be fused after being transferred to the sheet of support material rather than being successively fused.
With the advent of multi-color electrophotographic printing, it has become desirable to create copies having portions thereof color highlighted. For example, portions of the original document may be selected and reproduced on the copy in a color different than the remainder thereof. In this manner, the copy will have portions in one color and the remainder thereof in another color. An arrangement of this type would be highly useful for emphasizing selected paragraphs or portions of a letter. In this case, a selected paragraph or line could be highlighted in red or blue and the remainder thereof would be reproduced in black. Thus, the apparatus of the present invention is directed to producing a copy having portions thereof color accented.
Accordingly, it is a primary object of the present invention to improve electrophotographic printing so as to create copies having portions thereof color highlighted.